1. Field of the Invention
The subject invention relates to a core unit for a heat exchanger, and more specifically to a core unit bent relative to an axis perpendicular to a pair of headers such that the headers are bent.
2. Description of the Related Art
Various core units, shown generally at 10 in FIGS. 1 and 2, are known that include bends for fitting into smaller, more compact heating, ventilation, and air conditioning (HVAC) system cabinets. Core units 10 generally comprise a pair of headers 12 spaced from one another for receiving a fluid therein and having a plurality of apertures 14 for connecting a plurality of tubes 16. The tubes 16 are in fluid communication with the apertures 14 for transferring fluid between the headers 12. Fins 18 are disposed between adjacent pairs of tubes 16 for dissipating heat from the fluid in the tubes 16. The fins 18 are generally formed from sheet metal and are formed into a shape of an accordion. The fins 18 may be referred to as corrugated fins or air centers. The fins 18 may also be louvered, i.e., the fins 18 have louvers defined therein to increase heat transfer as is understood by those of ordinary skill in the art.
The core units 10 can be orientated in the HVAC system in various positions. In one orientation of the core unit, the tubes 16 are horizontal and the fins 18 are generally vertically aligned and transverse relative to the tubes 16. Because the convolutions of the fins 18 are up and down and the tubes 16 are horizontal, condensate may collect in the convolutions resulting in inadequate drainage. The condensate accumulation increases the air pressure drop and decreases performance of the core unit. The blockage can also result in ice formation during heat pump heating modes.
Further, it is known to bend the core units 10 so that the core units 10 fit within the cabinet. Generally, the core units 10 are bent about an axis that is parallel to the headers 12 such that the headers 12 are not bent. Bending the core unit in this manner slightly elongates the tubes 16 and only a minimal amount of fins 18 become crushed. The overall performance of the core unit is maintained with such an orientation. Also, the condensate accumulation is still likely to occur when the core unit is positioned having the tubes 16 horizontal.
One solution to overcoming the inadequate drainage is to orientate the core unit such that the tubes 16 are vertical and the fins 18 are generally horizontal and transverse to the tubes 16. The condensate is less likely to collect between the convolutions of the fins 18 when the tubes 16 are vertically aligned.
Prior attempts have been made to bend the core unit about an axis perpendicular to the headers 12 when the tubes 16 are vertical. However, when the core unit is bent, the tubes 16 and fins 18 next adjacent the bend undergo reduced performance. When the header is bent, as shown in FIG. 1, on the inner radius of the bend, the fin between adjacent tubes 16 is crushed thereby reducing and/or preventing fluid flow through the fin. Further, the fins 18 spaced from the axis of the bend may also be crushed as a result of the stress from the force required to bend the headers 12. Air pressure drop increases as a result of the fin collapsing and the thermal performance of the tubes 16 adjacent the crushed fin also is reduced. Experimentally it was determined that bending the headers 12 resulted in approximately fifty percent of fins 18 exhibiting some crushing and therefore lessened thermal properties. The outer radius of the bend, shown in FIG. 2, stretches the fins 18 and stresses the tubes 16 adjacent the bend, which is also undesirable.
The related art core units and methods of forming the same are characterized by one or more inadequacy. Accordingly, it would be advantageous to provide a core unit and a method of forming the same that overcomes these inadequacies.